1. Field of the Invention
The present invention generally relates to a storage, apparatus employed in a computer and/or a peripheral device of a computer. More specifically, the present invention is directed to a storage apparatus capable of preventing an oscillation phenomenon of a built-in servo mechanism.
2. Description of the Related Art
The storage apparatus as described above is, in general, known as, for instance, a magnetic-disk apparatus. A typical magnetic-disk apparatus is disclosed in, for example, Japanese KOKAI (Disclosure) Patent Application No. 60-101777 (1985). FIG. 1 is a side view of this magnetic-disk apparatus. Constructions of the magnetic-disk apparatus will now be described. In FIG. 1, reference numeral 1 denotes a supporting plate as a base; 2 is a rotating apparatus, e.g., a spindle motor attached on the supporting plate 1; 3 a recording medium, e.g., a magnetic disk attached to a rotating shaft of the rotating apparatus 2; 4 a head, e.g., a magnetic head arranged so as to face the recording plane or track, e.g., the lower plane of the recording medium 3; 5 a pressure spring to press the head 4 to the recording surface; 6 an arm to support one end of the pressure spring 5; and 7 an actuator to move and position the head 4 in the radial direction of the recording medium 3. The actuator 7 comprises: a carriage 8 to support and fix one end of the arm 6; a bearing 9 to guide and move the carriage 8 on the supporting plate 1; a cylindrical coil 10 attached to one end of the carriage 8; a magnet 11 arranged so as to face the coil 10; and a yoke 12 to position the magnet 11. Reference numeral 13 denotes a positioning sensor to detect the position of the head 4. The positioning sensor 13 comprises: a head speed converter 14 such as a photo diode fixed to the supporting plate 1; and an optical linear scale 15 attached to the carriage 8.
FIG. 2 is a block diagram showing a circuit of a drive control section in the magnetic-disk apparatus of FIG. 1. In FIG. 2, reference numeral 16 denotes a head speed demodulator for differentiating and shaping position information from the sensor 13 and thereby detecting a positioning speed of the head 4 in conjunction with the above-described head speed converter 14 and linear scale 15. Reference numeral 17 denotes a servo circuit for receiving a positioning command from a computer 19 and driving the actuator 7 while comparing the position information from the sensor 13 with speed information from the head speed demodulator 16.
Reference numeral 18 denotes a read/write circuit to record (write) or reproduce (read out) information to/from the recording medium 3 through the head 4. The computer 19 outputs a transport positioning command to the servo circuit 17 and also outputs a recording/reproduction command to the read/write circuit 18.
The operations of the magnetic-disk apparatus shown in FIG. 1 and the conventional storage apparatus shown in FIG. 2 will now be described. When the recording medium 3 is rotated by the rotating apparatus 2, a buoyancy occurs to the head 4 by the viscosity air flow on the surface of the recording medium 3. Since the buoyancy to the head 4 is balanced to the pressing force of the pressure spring 5, the recording medium 3 continuously rotates with a micro air gap held between the medium 3 and the head 4. When the transport positioning command is output from the computer 19 to the servo circuit 17, a current flows through the coil 10 and the force due to the Fleming's left-hand law acts on a magnetic circuit constructed of the magnet 11 and yoke 12. Therefore, the carriage 8 is driven and the head 4 is moved and positioned while seeking the information tracks which are coaxially arranged on the recording medium 3 at predetermined intervals in the radial direction (along the horizontal direction in FIG. 1). At this time, the servo circuit 17 positions the head 4 to the commanded position on the basis of the position information derived from the sensor 13. After completion of the transportation and positioning of the head 4, a recording/reproduction command is output from the computer 19 to the read/write circuit 18. The head 4 records or reproduces information to/from the recording medium 3. The positioning of the head 4 is performed by a servo mechanism constructed of the servo circuit 17, actuator 7, sensor 13, and head speed demodulator 16 on the basis of an ordinary automatic control theory. For instance, as snown in Hasegawa and Takai, "FOUNDATION AND APPLICATION OF AUTOMATIC CONTROL", (Jikkyo Technical Engineering Books), page 248, a gain margin of several dB is needed to make the servo mechanism stably operate.
In the conventional storage apparatus, the actuator 7 and sensor 13 are constructed by assembling mechanical parts. Therefore, there are problems such that a mechanical oscillation phenomenon occurs due to fluctuations of component quality or variations in assembly, so that the gain margin is reduced, the servo mechanism becomes unstable, the oscillation phenomenon is caused, and the head 4 cannot be positioned to the desired position of the recording medium 3.
The present invention is made to solve such conventional problems and it is an object of the invention to provide a storage apparatus which can prevent the oscillation phenomenon of a servo mechanism by way of electronic means.